The inside of a bowl of a decanter centrifuge, and centrifuges generally, is required to be cleaned occasionally prior to start up or after use in order to remove the materials which have accumulated along the bowl wall and have not been discharged. Preferably, this clean up is performed without disassembly of the centrifuge.
A decanter type centrifuge generally comprises a rotatable bowl and a screw conveyor mounted coaxially therein. The bowl typically includes a cylindrical section and a tapered end. The screw conveyor is adapted to rotate at a relative speed with respect to the bowl in order to cause discharge of the heavier material separated by the centrifugal forces. Clearance is provided between the inside bowl wall and the periphery of the conveyor flights. The material that settles in this- clearance area, called the heel, is not discharged by the conveyor and is compacted onto the inside bowl wall. The heel and the other materials that remain in the bowl after use are commonly required to be cleaned from the bowl at various times in order to prolong the operational life of the centrifuge. Centrifuges of this general type may be cleaned by the method disclosed in U.S. Pat. No. 4,036,426 to T. H. Little. This Little patent is incorporated herein by reference.
Typically a centrifuge requires specifically designed starters and motors to accelerate the bowl to full speed at start up. These special motors commonly require a larger than standard frame size and have long rotors in order to dissipate the excessive heat generated during acceleration. The motor temperature rise and the starter capabilities are the primary limiting factors in the time it takes to accelerate a centrifuge at start up. These factors may add significant size and cost to the motor used for rotating the bowl during normal operation.
U.S. Pat. No. 4,327,862 to W. Jakobs shows a decanter centrifuge having a first and second drive motor for rotating the bowl and the conveyor portions, respectively. The conveyor is driven by the second motor through a planetary gear box. The housing of the planetary gear box is connected to the centrifuge bowl such that during normal operation the conveyor and the bowl are operated at a differential RPM by the two motors. A switchable coupling is provided to connect the input of the planetary gear box to its housing during start up and then to selectively disengage the housing from the input of the planetary gear box after operating speed is attained. The second drive motor is used to drive the bowl and the conveyor during start up. The first drive motor is energized after the bowl has reached operational speed and after the coupling has disengaged the planetary gear box from the housing. The first drive motor continues to rotate the bowl during normal operation while the second motor controls the relative speed of the conveyor through the gear box.
U.S. Pat. No. 4,073,431 to E. A. Jager, shows a decanter centrifuge having a coupling between the bowl and the conveyor to adjust the differential RPM. The coupling is in the form of a hydraulic motor capable of breaking the speed of the conveyor with respect to the bowl during rotation. The conveyor break may be applied to completely stop the conveyor rotation to flush the bowl of the centrifuge.
U.S. Pat. No. 2,919,848 to A. F. Howe shows a decanter centrifuge having an electromagnetic break to adjust the conveyor differential speed. A clutch is also provided to assist in accelerating the conveyor during initial start up. U.S. Pat. No. 4,129,249 to Todd also shows the use of an electromagnetic control element to adjust the differential speed of the conveyor.
U.S. Pat. No. 4,069,966 to Crosby et al. shows a decanter centrifuge having a friction disk for adjustable damping of the centrifuge drive shaft to suppress chatter.
Russian Pat. No. 1025458 shows a torque limiting coupling connected to the output shaft of the reduction gear box and includes two friction discs intended for damping the torsional vibration of the screw conveyor therein.
U.S. Pat. No. 4,155,503 to Sears shows a nondecanter centrifuge having knives as a discharge means. A break is utilized to fix the knives within the bowl during discharge. This patent is generally representative of a series of patents which show non-decanter type centrifuges having clutch elements therein, including U.S. Pat. Nos. 1,230,560 to Camp; 2,453,791 to Harstick; and 2,655,241 to Hultberg.
U.S. Pat. No. 4,581,009 to Kramer and U.S. Pat. No. 4,113,171 to Cyphelly show hydraulic motors for controlling the differential speed of the conveyor with respect to the bowl of a decanter centrifuge.